package com.springboot.fram.core.digest.codec;

/**
 * Base32编码
 *
 * @author TaoYu
 */
public final class Base32 {

  private static final String BASE_32_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ234567";

  private static final int[] LOOKUP = {
      // '0', '1', '2', '3', '4', '5', '6', '7'
      0xFF, 0xFF, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F,
      // '8', '9', ':', ';', '<', '=', '>', '?'
      0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
      // '@', 'A', 'B', 'C', 'D', 'E', 'F', 'G'
      0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
      // 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O'
      0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E,
      // 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W'
      0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
      // 'X', 'Y', 'Z', '[', '\', ']', '^', '_'
      0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
      // '`', 'a', 'b', 'c', 'd', 'e', 'f', 'g'
      0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
      // 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o'
      0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E,
      // 'p', 'q', 'r', 's', 't', 'u', 'v', 'w'
      0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16,
      // 'x', 'y', 'z', '{', '|', '}', '~', 'DEL'
      0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
  };

  private Base32() {
  }

  /**
   * 编码
   *
   * @param source 被编码的base32字符串
   * @return 被加密后的字符串
   */
  public static String encode(String source) {
    return encode(source.getBytes());
  }

  /**
   * 编码
   *
   * @param bytes 数据
   * @return base32
   */
  public static String encode(final byte[] bytes) {
    int i = 0, index = 0, digit = 0;
    int currByte, nextByte;
    StringBuilder base32 = new StringBuilder((bytes.length + 7) * 8 / 5);

    while (i < bytes.length) {
      currByte = (bytes[i] >= 0) ? bytes[i] : (bytes[i] + 256);
      if (index > 3) {
        if ((i + 1) < bytes.length) {
          nextByte = (bytes[i + 1] >= 0) ? bytes[i + 1] : (bytes[i + 1] + 256);
        } else {
          nextByte = 0;
        }
        digit = currByte & (0xFF >> index);
        index = (index + 5) % 8;
        digit <<= index;
        digit |= nextByte >> (8 - index);
        i++;
      } else {
        digit = (currByte >> (8 - (index + 5))) & 0x1F;
        index = (index + 5) % 8;
        if (index == 0) {
          i++;
        }
      }
      base32.append(BASE_32_CHARS.charAt(digit));
    }

    return base32.toString();
  }


  /**
   * 解码
   *
   * @param base32 base32编码
   * @return 数据
   */
  public static byte[] decode(String base32) {
    int i, index, lookup, offset, digit;
    byte[] bytes = new byte[base32.length() * 5 / 8];

    for (i = 0, index = 0, offset = 0; i < base32.length(); i++) {
      lookup = base32.charAt(i) - '0';
      if (lookup < 0 || lookup >= LOOKUP.length) {
        continue;
      }
      digit = LOOKUP[lookup];
      if (digit == 0xFF) {
        continue;
      }
      if (index <= 3) {
        index = (index + 5) % 8;
        if (index == 0) {
          bytes[offset] |= digit;
          offset++;
          if (offset >= bytes.length) {
            break;
          }
        } else {
          bytes[offset] |= digit << (8 - index);
        }
      } else {
        index = (index + 5) % 8;
        bytes[offset] |= (digit >>> index);
        offset++;

        if (offset >= bytes.length) {
          break;
        }
        bytes[offset] |= digit << (8 - index);
      }
    }
    return bytes;
  }

}
